Solar cells can be a viable energy source by utilizing their ability to convert sunlight to electrical energy. Silicon is a semiconductor material and the raw incoming material used in the manufacture of solar cells; The electrical properties of the cells, namely the conversion efficiency depends critically on the purity of the Silicon. Several techniques have been used to purify Silicon. The most well known technique is called ‘Siemens process’. This technique allows to almost remove every single impurity present within the Silicon. However, this technique requires to produce the silicon into a gas phase and redeposit into a solid phase in order to remove the impurities. The technique describes in this patent allows to remove very effectively impurities by melting the Silicon into a liquid phase and solidifying the Silicon using a technique called ‘directional solidification’. While this technique is very well known, this patent focuses on a new way to use the directional solidification that allows to reduce considerably the cost of this procedure.
Techniques used to make purified silicon crystals for solar cells are known. Most of these techniques operate on the principle that while silicon crystals are solidifying from a molten silicon solution, undesirable impurities remain in the molten solution. A first example technique, the float zone technique, can be used to make silicon monocrystalline ingots using a moving liquid to urge impurities toward an edge of a mold for removal. Another example technique, the Czochralski technique, can be used to make silicon monocrystalline ingots using a seed crystal that is slowly pulled out of a molten solution, allowing the formation of a monocrystalline column of silicon while leaving impurities in the solution. Further example techniques, such as the Bridgeman or heat exchanger techniques, can be used to make silicon multicrystalline ingots through the creation of a temperature gradient with a controlled cooling rate, causing directional solidification.